We have extended our previous work on the topology of membrane components involved on the expression of chemically-homologous domains at the surface of mammalian cells. As we did in the past, we have used a highly polorized cell (spermatozoa) where regionalization of surface components is extreme. In these cells, the distribution of receptors of lectins (concanavalin A, and wheat germ agglutinin) in plasma and acrosomal membranes was determined in preparations obtained by the "fracture-label" method, conventional freeze-fracture, and surface labeling. Sites of lectin attachment to the membrane were visualized by electron microscopy using protein-coated colloidal gold as the cytochemical marker. In addition to our previous results we show that: a. stable surface domains formed by specific glycoconjugates are primarly conditioned by transmembrane glycoproteins; b. regionalization of glycoconjugates may also occur in intracellular membranes, as we have demonstrated in the acrosomal membrane (where Con A receptors are accumulated in the equatorial segment); c. current methods of membrane fractionation, as well as conventional cytochemical techniques may lead to data on the topology of specific components of intracellular membranes that is tainted by the presence of contaminants.